The present invention relates to novel luminescent materials or phosphors based on organic compounds having an internal torsion leading to an excited state by charge transfer to the lowest fluorescent level.
For some years now, research has been carried out on different organic molecules and it has been found that certain molecules dissolved in polar solvents can give rise to double fluorescence phenomenon when they have a structure with an internal torsion and can lead to a charge transfer.
Molecules of this type are more particularly described by W. RETTIG in Journal of Luminescence, 26, 1980, pp. 21-46; G. WERMUTH et al in Ber. Bunsenges, Phys, Chem. 85, 1981, pp. 64-70; Z. R. GRABOWSKI et al in Pure and Appl. Chem., Vol. 55, No. 2, pp. 245-252, 1983; and RETTIG et al, Chem. Phys., Letters, Vol. 87, No. 3, 1982, pp. 229-234.
The double fluorescence phenomenon of compounds of this type, is generally explained by the fact that in the excited state the molecule can be transformed by the internal rotation of a group, such as --N(alkyl).sub.2. Thus, this excited state corresponds to a conformation isomer which is able to transfer charges and hereinafter this excited state with internal torsion and charge transfer is called "TICT", an acronym for "twisted intramolecular charge transfer", used in the art to identify such phenomena.
Following research relating to these molecules dissolved in different solvents, it was found that the appearance of the excited state was aided by dipole-dipole interactions with the solvent and by reducing the viscosity of the solution. In addition, it has not hitherto been envisaged to include such molecules in solid matrixes.